In recent years it has become common to provide portable data storage devices having an internal flash memory. Such a device is disclosed in PCT/SG00/00029, entitled “Portable Data Storage Device”. There a portable storage device is described having an integral USB plug which plugs into a USB socket of a computer (or other device). The portable data storage device includes a flash memory for storage of user data. The size of the memory in commercial versions of this device is typically at least 8 MB, but is often much higher. The overall size of the device is typically small enough that it fits into a closed fist.
Typically, commercial versions of this device employ NAND flash memory. NAND flash memory is available in two types: single layer cell (“SLC”) flash memory, and multiple level cell (“MLC”) flash memory. SLC presently has higher read/write speeds and longer lifetime, but MLC, which makes possible the storage of more than one (typically, two) bits per cell, is cheaper per bit stored.